1. Field of the Invention
The present invention generally relates to electrical power distribution systems. In particular, the present invention relates to splices used in such distribution systems.
2. Description of the Related Art
In a typical electrical power distribution system, there exist various methods and systems for joining power distribution cables. For example, two cable conductors may be joined or spliced together by using a metallic connector that joins the two cable conductors together, and a splice housing that covers and encloses the metallic connector. The splice housing is typically composed of: (i) an internal Faraday shield around the metallic connector and any internal air spaces; (ii) insulation surrounding the internal Faraday shield, the insulation being of suitable material and thickness for typical voltage class systems of 5, 15, 25 or 35 kV; and (iii) an external semi-conductive shield. Additional metallic components can be used during splicing to restore the cable metallic shielding, and end seals can be provided to prevent water migration under the cable jacket.
Many of the current splicing systems contain the above components as either several different components or as a unified single splice housing unit and the metallic connector. An example of a drawback of having more components is the increase in installation errors and decrease in reliability. Typically, the metallic connect is standardized but there may be multiple types of splice housings.
An example of a splice housing is a tape splice housing where, after two cables are joined with the metallic connector, the splice housing is constructed by hand-taping sequential layers of both conductive and insulating tapes. An example of a drawback to the tape splice housing is the long length of time it takes to construct the splice housing and the high skill requirement of the splicer constructing the splice housing.
Another example of a splice housing is an interference fit push on. The push-on housing is initially stored onto one of two cables prior to connecting the two cables. After the metallic connector is installed, the push-on housing is pushed and installed over the metallic connector and cable ends. Drawbacks include the installation force necessary to store and position the housing and the need for many different size housings to cover different cable sizes, as well as the difficulty of incorporating end seals.
Another example of a splice housing is a heat shrinkable splice housing. The heat shrinkable housing is initially stored onto one of two cables prior to connecting the two cables. After the metallic connector is installed, the heat shrinkable splice housing is slid over the connector and cable ends. The heat shrinkable splice housing is then reduced in size by applying heat, until the heat shrinkable housing shrinks completely in place. An example of a drawback to the heat shrinkable splice housing is the necessity of using a torch or other heat-applying device, which can be dangerous, particularly within the enclosed spaces of manholes and the like where electrical distribution cables are typically found. Another drawback is that the application of heat requires a technician with a high level of skill in order to ensure that the heat shrinkable tubes of the housing are uniformly formed and adequately shrunk. A further drawback is that the technician also ensures that sufficient heat is used to activate the heat shrinkable housing tubes and sealing materials, yet that not too much heat is applied that would otherwise damage any materials or the cable insulation.
Another example of a splice housing is a cold shrinkable splice housing. The cold shrinkable housing is initially stored onto one of two cables prior to connecting the two cables. After the connector is installed, the cold shrinkable housing is slid back over the connector and cable ends. A support core is removed from one end (or removed from each end in the case of a two-piece support core) allowing the insulating housing to constrict over the connector and cable ends. The support tube(s) of the cold shrinkable housing can be a solid-type core, a spiral core or a friable core. The cold shrinkable housing can also be sealed with a seal material in order to provide the proper environmental sealing. Sealing materials are typically composed of a mastic of putty consistency, for example a butyl. The sealing material is usually applied to the cable insulation ends prior to pulling the expanded tube into position, although the preferred method, as a result of foreseeable workmanship mistakes, would be to have the sealant pre-installed under the removable core. However, maintaining the position of the core during removal is problematic.
An example of a drawback to the cold shrinkable housing is that as the insulating tube increases in length so too must the support core, which may cause problems. For example, the removal of a long core is time-consuming and creates ergonomic issues. Furthermore, the support cores are typically rigid along their entire length, requiring large storage facilities to allow the cores to be stored perfectly straight. When a spiral core is used, the spiral core must be unwound when removed in order to prevent jamming. A drawback to this is that it is difficult to keep the sealing mastic in place if included under the pre-stretched unit. Furthermore, spiral cores require the shrinkable tube to be expanded more than is required of a solid core to allow easy removal of the core. In the case of designs using a central, non-removable support core and only short spiral cores on the ends, there must be a method of removing or wicking heat off of the connector since an air space is left between the non-removed support core and the connector. Also, when a solid core is used, the solid support core requires an auxiliary film between the shrinkable tube and the support core to aid in easy removal. The length of these support cores depends on whether it is a single unit removed from one end or two separate cores removed from each end.
Other major drawbacks of the current heat and cold shrinkable splice housing designs include the need for the housing conductive materials and insulating materials to be identical throughout the length of the tube or tubes. However, since the conductive and insulating materials serve different purposes, this requirement leads to compromises in the required properties of the materials. Furthermore, for the current heat and cold shrinkable splice housing designs, there is presently no technique for incorporating a test point for testing the transmission circuit of the cable system for an energized condition. This is dangerous because the determination of whether or not the cables are energized can lead to a determination as to whether or not the circuit may electrocute a user.
In light of the shortcomings of the conventional methods and applications known in the art, it is desirable to provide a splice housing that allows for smaller core centers, flexibility in the material parameters, and insertion of testing points to determine whether the cable circuit is energized.